There is a general need in the field of civil engineering to instrument structures such as roads, bridges, tunnels and the like with sensors such as wireless sensors, to monitor movement/integrity of the structure. This facilitates, among other things, efficient maintenance and improved safety. It is helpful if such a sensor has wireless communications; it may be battery powered or powered solely by, or supplemented by, energy harvesting. However it is also desirable to be able to achieve a long battery life, although the RF environment is often challenging, with poor signal propagation. Current devices are physically large, with a typical dimension of order 10 cm, and have a limited battery life, for example of order 2-3 months. Considerable improvement is possible by judicious selection of RF frequency (for example 400-900 Mghz is helpful), and selective sensor activation, providing sleep and deep-sleep modes. The use of low power processor technology, such as that available from ARM Ltd (UK) can also help to reduce power consumption. However even when all of these techniques are combined significantly losses still remain, with surprising origins.
The use of miniature, low power technology to instrument civil engineering structures brings other difficulties: it is generally desirable to provide a large number of sensors so that a structure can be closely monitored and relative motion of various parts of the structure identified for assessments/action. This often entails programming individual sensors indifferent ways—some may sense motion, some temperature, some humidity, some a combination of all three. These different types of sensors may be arranged over the structure in an optimum manner so that, for example, readings from different sensors may be interpolated/extrapolated. Such an approach generally entails programming different sensors with different software, depending upon the measurement made. However programming each individual sensor may take a significant amount of time, for example of order half an hour (depending upon various factors). When instrumenting a structure with a large number of sensors this programming time constitutes a significant practical problem.
New techniques have therefore been developed to address these difficulties. Although they are particularly useful when instrumenting a structure with sensors, the techniques we describe are not limited to such applications and, potentially, have more general value.